Problem: Simplify the following expression: $k = \dfrac{r}{3} \div \dfrac{9r}{10}$
Explanation: Dividing by an expression is the same as multiplying by its inverse. $k = \dfrac{r}{3} \times \dfrac{10}{9r}$ When multiplying fractions, we multiply the numerators and the denominators. $k = \dfrac{ r \times 10 } { 3 \times 9r}$ $k = \dfrac{10r}{27r}$ Simplify: $k = \dfrac{10}{27}$